The Thriving at Work report, published on Thursday, puts the annual cost to the UK economy of poor mental health at up to £99bn, of which about £42bn is borne by employers.

The authors – the Mind chief executive, Paul Farmer, and the mental health campaigner and a former HBOS chair, Dennis Stevenson – said they were shocked to find the number of people forced to stop work as a result of mental health problems was 50% higher than for those with physical health conditions.

Farmer said the evidence suggested it is still a taboo subject in many workplaces. “The picture is that there are very significant numbers of people in work with mental health problems but there are significant numbers who are not,” he said.

“We think that the reasons for that are a combination of a lack of support, lack of understanding within some workplaces and a lack of speedy access to mental health services. Sometimes in organisations people feel themselves excluded as a result of their mental health issues and sometimes people don’t necessarily spot that somebody is struggling.”

Farmer and Stevenson said that the challenge was bigger than they had envisaged when instructed by the prime minister, but that with action dramatic changes could be achieved over the next 10 years. They said they hoped that the number of people with long-term mental health problems who lose their jobs could be reduced to the same level as those with physical conditions.

They found that about 15% of people at work have symptoms of an existing mental health condition, which they said illustrates the fact that given the right support they can thrive in employment.

Farmer described the economic case as overwhelming and the authors link current failures to the UK’s relatively poor productivity. An analysis by Deloitte examining existing workplace interventions identified potential to generate a return to business of between £1.50 and £9 for every £1 invested.

Among examples of good practice highlighted by the report are the mental health first aid courses at Thames Water and, at Aviva, the promotion of e-learning modules to help identify and self-identify when people need support.

Farmer and Stevenson said they want all employers to commit to six core standards around mental health, including having a plan in place, increasing awareness among employees, stipulating line management responsibilities and routinely monitoring staff’s mental health and wellbeing. “What we feel is really important is that organisations take responsibility for the mental health of their staff,” said Farmer.

“As the stigma around mental health begins to shift, I think the area of mental health in the workplace is becoming much more visible. Employers are recognising that this is an issue, but they don’t know what to do. That’s why we’ve recommended these core standards.”

Highlighting further benefits for companies, he said that some young people were now asking employers about their mental health policies in the same way they might have asked about their green credentials a decade ago.

“The most progressive organisations in this area are already being quite open in terms of their internal reporting and what they put on their website in terms of how they support their staff,” he said.

Large employers are expected to go further and the report calls on the government and public sector to lead by example. It says the government should also ensure that the NHS provides high quality mental health services, quick and convenient to fit around employment, and consider enhancing protections for employees with mental health conditions in the Equality Act 2010.

The report makes 40 recommendations and Stevenson urged the government to accept them all. “We need the right leadership among employers in the public, private and voluntary sectors, and a mandate from policy-makers to deliver our ambitious but achievable plan,” he said.

Stephen Martin, director general of the Institute of Directors, welcomed the review which he said shows “mental health is not just a moral issue, but a business one too. Business leaders must put themselves at the frontier of addressing these challenges.”

Case study: ‘I was using work in a quite self-destructive way’

Andrew Omerod: ‘I’d been living with depression a very long time already; work happened to be the way it was expressed.’

Andrew Omerod, 35, from London, operations director at GrantTree, says he has experienced both sides of the coin when it comes to mental health problems at work. “When I was working for my previous employer, I was using work in quite a self-destructive way. Overworking is a way of acting out the pain you’re experiencing that you don’t know how to express. It’s also a way of escaping it in the short term – but it’s harmful in the long term.

“It was work that led to me having a breakdown. I’d been living with depression a very long time already; work happened to be the way it was expressed. I had to take time off, about a year.

“The thing that was disappointing for me more than anything else was that when I was ready to go to work my employer became quite disruptive. They basically said: ‘You can come back to us but rather than reporting directly to the MD [managing director] you’re going to have to report to someone else who we’ve promoted in your absence.’ So we agreed that I would leave.

“The experience at GrantTree has been very different. I am very passionate about my job, I get caught up in it and here I have colleagues who say to me: ‘You seem to be staying late and taking on quite a lot of stuff, is that sustainable?’ [They are] people who recognise I can fall into this kind of behaviour.”